1. Field of the Invention
The present invention relates to an improved method of recovering a synthetic substrate from a layer of material such as a recording layer applied on the substrate and a device that can be used in the above-mentioned method.
2. Description of the Related Art
Materials comprising layers having various functions applied on a substrate comprising a synthetic resin or an organic acid ester of cellulose are used in many fields. For example, various types of recording material comprising a recording layer, etc. applied on a substrate such as cellulose triacetate, poly(ethylene terephthalate) or polycarbonate are widely used in practice. These recording materials include photosensitive photographic materials comprising a silver halide photosensitive layer, CD-ROM, CD-R, DVD and DVD-R materials comprising a colorant recording layer or a reflective layer applied on a PMMA or polycarbonate substrate.
With regard to an example of a method of recovering the polycarbonate substrate from optical discs, there is a method disclosed in Japanese Patent Application Laid-open No. 4-360035 (Japanese Patent Publication No. 2615277) in which discs having an aluminum reflective layer are treated in a concentrated aqueous alkali solution at 75 to 100xc2x0 C. There is also a method disclosed in Japanese Patent Application Laid-open No. 5-345321 in which a plastic molding having a metal vapor deposition film is heated in hot water at 70xc2x0 C. or higher so as to peel off the vapor deposition film.
With regard to a washing device used for recovering the synthetic substrate from the above-mentioned recording materials, a device disclosed in Japanese Patent Application Laid-open No. 5-8228 is known. This device can efficiently wash a chip material in a short time and the washed chip material can be taken out in a short time without a complicated procedure. However, since it is not a pressure device, the maximum washing temperature is 100xc2x0 C. and reduction in the washing time and enhancement of the quality of the recovered substrate are thus limited. If an attempt is made to modify the above-mentioned chip washing device into a pressure vessel using a standard arrangement, the thickness of the flat end plate in the base needs to be a few centimeters. In the case where the end plate in the base is made in a hemispherical shape, although the end plate can be thin, a large dead space is formed in the base and not only does the size of the device increase but also the operability becomes very poor.
The present invention has been carried out in view of the above-mentioned circumstances, and it is a first object of the present invention to provide a method of recovering large quantities of a synthetic resin or an organic acid ester of cellulose (hereinafter, termed xe2x80x98synthetic resin, etc.xe2x80x99) and, in particular a polycarbonate substrate or a polyester substrate, with a quality that allows it to be reused in the original application, at a low recovery cost and in a stable manner. It is a second object of the present invention to provide a pressure type washing device that can be used in the above-mentioned recovery method.
In accordance with a first aspect of the present invention in order to achieve the above-mentioned objects, a method of removing a layer of material from a synthetic resin or an organic acid ester of cellulose, comprising: washing the layer from the substrate with an aqueous alkali solution with a temperature of at least 105xc2x0 C., and then washing the alkali solution from the substrate.
With regard to the above-mentioned synthetic resins, aromatic polycarbonates, aromatic polyesters and polypyromellitic imides are preferred, and bisphenol A polycarbonate, poly(ethylene terephthalate) and poly(ethylene naphthalate) are particularly preferred.
With regard to the organic acid esters of cellulose, cellulose acetate, cellulose acetate butyrate and cellulose acetate propionate are preferred.
In accordance with a second aspect of the present invention, a method of recovering a polycarbonate substrate is provided which comprises the steps of:
providing a polycarbonate substrate having at least one functional layer thereon, the functional layer, selected from the group consisting of a colarant containing layer, a metal reflective layer, a photosensitive layer, a protective layer an adhering layer and an undercoat layer;
applying an effective amount of an aqueous alkali solution with a pH of at least 10 and a temperature of at least 105xc2x0 C. to substantially remove the functional layer from the polycarbonate substrate; and then
washing the alkali solution from the substrate.
Furthermore, it is preferable to use the above-mentioned method of recovering a polycarbonate substrate comprising the steps of applying an aqueous alkali solution containing 0.1 to 20 wt % of a caustic alkaline and 0.001 to 10 wt % of a surfactant while stirring and then washing the alkali solution from the substrate and optionally drying. Moreover, with regard to the above-mentioned method of recovering a polycarbonate substrate, the washing step may comprise at least two steps of applying a different fresh aqueous alkali solution, or a step of washing at 100xc2x0 C. or below may be added before or afterwards. The method of recovering a polycarbonate substrate may comprise, followed by applying an aqueous alkali solution, a step of washing with an aqueous solution containing 0.1 to 10% of a peroxide, preferably a slightly acidic aqueous hydrogen peroxide solution.
A third aspect of the present invention relates to a method of recovering a polyester substrate including the steps of:
providing a polyester substrate having at least one functional layer thereon, the functional layer, selected from the group consisting of a silver halide photosensitive layer, a silver containing layer, a protective layer, and an undercoat layer;
applying an effective amount of an aqueous alkali solution with a pH of at least 10 and a temperature of at least 105xc2x0 C. to substantially remove the functional layer from the polyester substrate; and then
washing the alkali solution from the substrate.
The method of recovering a polyester substrate may include a step of pre-cutting if necessary a polyester substrate having at least one functional layer thereon, into chips and then treating them with a 0.1 to 3 wt % aqueous alkali solution of a temperature of 105xc2x0 C. to 150xc2x0 C.
A fourth aspect of the present invention relates to a device that can desirably carry out the above-mentioned recovery method and, in particular, a pressure type washing device comprising a pressure vessel comprising a longitudinal cylindrical body having a circular cross-section, an end plate connected to the top of the cylindrical body, an inverted end plate connected to the lower part of the cylindrical body in a manner such that its convex part faces upwards, the end plate having a lid and a washing liquid inlet, the lid allowing a chip material to be fed through, a chip outlet provided in the lower part of the body, a strainer plate traversing the cylindrical body provided in the lower inner part of the body, a stirring blade provided above the strainer plate in close proximity to the strainer plate, and a stirring shaft for the stirring blade provided so as to run through the inverted end plate.
The pressure type washing device of the present invention preferably has an end plate or an inverted end plate in the shape of an dished head. The ratio of the diameter D to the height H of the end plate or the inverted end plate is not particularly limited, but it is preferable that D:H=1:0.08 to 0.12
The above-mentioned pressure type washing device preferably includes a hollow core for filling the space formed between the strainer plate and the lower end plate and a pressure equalizing pipe for equalizing the pressure between the core and the pressure vessel.
Furthermore, the pressure type washing device of the present invention preferably includes a chip outlet having a clutch door connected to the cylindrical body, the clutch door being arranged so that a body ring forming a circular flange connected to the cylindrical body side and an end plate ring forming a circular end plate flange of an outlet cover face each other, the two rings being fixed by being clamped by an external ring.
The device of the present invention preferably includes a strainer plate which forms is a small angle of 10 to 30 degrees to a plane perpendicular to the central axis of the vessel. It is also preferable to provide the strainer plate with small pores having a diameter of 1 to 10 mm and an interval between the pore ends of 2 to 10 mm.
The cylindrical body preferably comprises a jacket for heating and cooling.
The ratio of the inner diameter D to the inner height H of the cylindrical body is not particularly limited, but it is preferable that D:H=1:1 to 2.5.
It has been difficult to obtain recyclable high quality synthetic resin, etc. (no foreign matter detected, no depolymerization) in a short time at low treatment cost using the various recovery methods and recovery devices known in the art but, in accordance with the recovery method of the present invention, synthetic resin substrate, etc. can be recovered for the first time with a high quality that allows it to be reused in the original application.
In accordance with the method of recovering synthetic resins, foreign matter on the substrate can be removed with a reduced amount of caustic alkali in a reduced treatment time at a lower cost. Furthermore, depolymerization of the substrate can be suppressed; it is also possible in some cases that low molecular weight components are removed so increasing the degree of polymerization of the substrate, and it is thus possible to easily recover reusable good quality polycarbonate substrate at a comparatively low cost.
Moreover, in accordance with the process of the present invention, merely by providing a cathode in the treatment liquid comprising an aqueous alkali solution and applying a low voltage (10 volts or below) the silver can be recovered from a natural resin or a synthetic resin containing silver or a silver salt without using any additive known in the art and the formation of silver-containing scale on the treatment vessel can be suppressed.